SPARQL เอกสารหล ก ใน มคอ.3

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1 SPARQL SLIDES REFERENCE: SEMANTIC WEB PRIMER BOOK เอกสารหล ก ใน มคอ.3

2 Why an RDF Query Language? Different XML Representations XML at a lower level of abstraction than RDF There are various ways of syntactically representing an RDF statement in XML Thus we would require several XPath queries, e.g. //uni:lecturer/uni:title if uni:title element //uni:lecturer/@uni:title if uni:title attribute Both XML representations equivalent! 2

3 SPARQL Basic Queries SPARQL is based on matching graph patterns The simplest graph pattern is the triple pattern : -like an RDF triple, but with the possibility of a variable instead of an RDF term in the subject, predicate, or object positions Combining triple patterns gives a basic graph pattern, where an exact match to a graph is needed to fulfill a pattern

4 Examples PREFIX rdf: < PREFIX rdfs: < SELECT?c WHERE {?c rdf:type rdfs:class. } Retrieves all triple patterns, where: -the property is rdf:type -the object is rdfs:class Which means that it retrieves all classes

5 Examples (2) Get all instances of a particular class (e.g. course) : (declaration of rdf, rdfs prefixes omitted for brevity) PREFIX uni: < SELECT?i WHERE {?i rdf:type uni:course. }

6 Using select-from-where As in SQL, SPARQL queries have a SELECT-FROM-WHERE structure: SELECT specifies the projection: the number and order of retrieved data FROM is used to specify the source being queried (optional) WHERE imposes constraints on possible solutions in the form of graph pattern templates and boolean constraints Retrieve all phone numbers of staff members: SELECT?x?y WHERE {?x uni:phone?y.} Here?x and?y are variables, and?x uni:phone?y represents a resourceproperty-value triple pattern 6

7 Implicit Join Retrieve all lecturers and their phone numbers: SELECT?x?y WHERE {?x rdf:type uni:lecturer ; uni:phone?y. } Implicit join: We restrict the second pattern only to those triples, the resource of which is in the variable?x Here we use a syntax shorcut as well: a semicolon indicates that the following triple shares its subject with the previous one 7

8 Implicit join (2) The previous query is equivalent to writing: SELECT?x?y WHERE {?x rdf:type uni:lecturer.?x uni:phone?y. }

9 Explicit Join Retrieve the name of all courses taught by the lecturer with ID SELECT?n WHERE {?x rdf:type uni:course ; uni:istaughtby : ?c uni:name?n. FILTER (?c =?x). } 9

10 Optional Patterns <uni:lecturer rdf:about= > <uni:name>grigoris Antoniou</uni:name> </uni:lecturer> <uni:professor rdf:about= > <uni:name>david Billington</uni:name> </uni:professor> For one lecturer it only lists the name For the other it also lists the address 10

11 Optional Patterns (2) All lecturers and their addresses: SELECT?name? WHERE {?x rdf:type uni:lecturer ; uni:name?name ; uni: ? . } 11

12 Optional Patterns (3) The result of the previous query would be: Grigoris Antoniou is listed as a lecturer, but he has no address?name? David Billington david@work.example.org 12

13 Optional Patterns (4) As a solution we can adapt the query to use an optional pattern: SELECT?name? WHERE {?x rdf:type uni:lecturer ; uni:name?name. OPTIONAL { x? uni: ? } } 13

14 Optional Patterns (5) The meaning is roughly give us the names of lecturers, and if known also their address The result looks like this:?name Grigoris Antoniou David Billington? 14

15 Summary RDF provides a foundation for representing and processing metadata RDF has a graph-based data model RDF has an XML-based syntax to support syntactic interoperability XML and RDF complement each other because RDF supports semantic interoperability RDF has a decentralized philosophy and allows incremental building of knowledge, and its sharing and reuse 15

16 Summary (2) RDF is domain-independent - RDF Schema provides a mechanism for describing specific domains RDF Schema is a primitive ontology language It offers certain modelling primitives with fixed meaning Key concepts of RDF Schema are class, subclass relations, property, subproperty relations, and domain and range restrictions There exist query languages for RDF and RDFS, including SPARQL 16

17 LINKED OPEN DATA

18 Linked Open Data Slides Reference:

19 What is now User generated content is growing tremendously Isolated contents need deadly to get connected. The world is connected, so do the data, information and knowledge

20 Old terms Data -- sensing the world What you sense (see, hear, smell, touch ) Information perceiving the world Perceive the sensed data Knowledge contextualizing information Comprehend the perceived information Add context Context ultimately determines what s actually what.

21 What is our daily life Access data Manipulate data (add, delete, change) Process data Generate information (tables, forms) Create knowledge (reports, papers..)

22 Data is our life Data is our daily bread Do we have identifier for data? Not really important if data is small and individual Really important if data is huge and connected? Should we need identifier for our data? Why do we need our name, or social security number? Can you refer to someone without identifier?a person with good heart----

23 Make our busy life less messy We just got 24 hours per day, not more Add identifier to our data Give the everyone-agreed-unique-identifier to each data -- the perfect world of our dreamland We will not have any integration problem, most of the IT departments can be closed Different groups give different identifiers to the same data we can live with that, it is more real in our daily life, standardization bodies and IT guys are helping us. We are happy that we can refer to data

24 Where are our data In computer On the Web In my paper notes In printed books Data are being digitalized and are available online Web Data

25 Web data Data on the Web Online journal Blog Wiki Data in physical world Yourself Table Book in library Computer you are using The boundary is blurring Paper is both in your hand and on the Web

26 How to refer data Web data DOI (Digital Object Identifier) OpenID (people, ) URI (blog, wiki, homepage, )

27 URI (Uniform Resource Identifier) To identify or name a resource on the Internet The main purpose is to enable interaction with representations of the resource over a network, typically WWW, using specific protocols from Wikipedia URN like a person s name urn:isbn: Book of Romeo and Juliet URL like a street address

28 Linked Data A term coined by Tim Berners-Lee It describes HTTP-based Data Access by Reference for the Web Current web is changing from hypertext links (link documents) to hyperdata links (linking data) Data are small components of the resources It drills deep to the details of the resources Linked data provides a powerful mechanism for meshing disparate and heterogeneous data

29 Vision from Sir Berners-Lee The Semantic Web isn t just about putting data on the web. It is about making links. Four Rules for linking data Use URIs as names for things Use HTTP URIs so that people can look up those names When someone looks up a URI, provide useful information (URI dereferencing) Include links to other URIs, so that they can discover more things Breaking them does not destroy anything, but misses an opportunity to make data interconnected. This in turn limits the ways it can later be reused in unexpected ways. It is the unexpected re-use of information which is the value added by the web

30 W3C SWEO Linking Open Data Project Project aims to Publish existing open license datasets as linked data on the web Interlink things between different data sources Develop clients and applications that consume linked data from the web

31 Bubbles in May 2007 Over 500M RDF triples Around 120K RDF links between data sources

32 Bubbles in April 2008 >2B RDF triples Around 3M RDF links

33 2011

34 2017

35 What are Linked Data? Linked Data require RDF Why not XML? Different model theory But not all RDF data are linked data You have to compliant your RDF data according to the four rules mentioned by Berners-Lee

36 linked data Linked data are just RDF triples <rdf:description about= > <fam:haschild rdf:resource=" <fam:haschild rdf:resource=" </rdf:description> How can I get RDF triples Relational database: D2R tools can convert them for you RDFizers from SIMILE: Can convert JPEG, MARC/MODS, OAI-PMH, OCW(MIT Open Course), , BibTex, Java, Javadoc, etc. to RDF

37 Thumb of the rules Understand your data What do you want to have in your data Do not reinvent REUSE! Potential ontologies/vocabularies FOAF, Dublin Core, SKOS URI Aliases Different URIs for the same non-information resource (Berlin, etc.) owl:sameas to link these URI aliases

38 More principles Linked Data is simply about using the Web to create typed links between data from different sources. The principle of Linked data is to: Use the RDF data model to publish structured data on the web Use RDF links to interlink data from different data sources. Use HTTP URIs to identify resource To avoid other URI schemes (URNs or DOIs)

39 Power of Linked Data ying foaf:name Ying Ding rdf:type foaf:person dblp:publications foaf:publication foaf:knows Stefan 72K foaf:based_near dp:population db:galway dp:dublin skos:subject skos:subject dp:cities_in_ireland

40 What LOD can bring? It will lift current document web up to a data web LOD browsers can let you navigate between different data sources by following RDF links. It can drill down to the lower granularity of the information allowing you for more fine search on the web making the question-answer search on the Web possible meshing up different data through RDF links Making the built-on-top application easier

41 Document Web vs. Data Web Document Web Glued by hyperlinks Data are HTML pages Query result is HTML pages, which can not be further processed Data are just interlinked, but not integrated Data access through different APIs Data Web Glued by RDF links Data are RDF triples Query result is RDF triples which can be easily further processed (e.g., web services) Data are interlinked and integrated, and links are typed Data access through a single and standardized access mechanism (maybe it will called in the future LOD API?)